Dermis and most other human tissues contain two major types of collagen molecules -- alpha 1(I) 2 alpha 2 and alpha 1(III)3. The latter has not been extracted by the usual solvents and so human tissues have been digested with pepsin. This liberates a mixture of the two types of collagen, the molecules being nearly intact. Differential salt precipitation separates the two types, and they differ chromatographically and in their amino acid composition. The three alpha 1(III) chains are bound together by disulfide links, and adjacent molecules are probably also cross-linked by such bonds. Cyanogen bromie peptides of the alpha 1(III) chains are being characterized and the distribution of this collagen in different organs and within tissues is being studied under normal as well as pathological conditions.